Although most of the frequency spectra capable of supporting wireless communications is regulated by various governments and is subject to licensing or permitting, certain frequency ranges have been designated as being unlicensed spectrum. In these “unlicensed” bands, low-energy operation (typically 1 Watt or less, and often 100 mW or less) is permitted without a license. At least some of these bands may also be referred to as the industrial, scientific, and medical equipment (ISM) bands, and in the U.S. include the ranges of 902 to 928 MHz, 2.4 to 2.4835 GHz, and 5.725 to 5.875 GHz. Other frequency ranges, such as 24 GHz and 60 GHz are also available for unlicensed use as well. Additional frequency ranges, such as 802.11af operating in the 470-710 MHz range, and 802.11ad, operating in the 57-64 GHz range are also presently being developed.
Such unlicensed spectrum has sparked a revolution in wireless technology, and multiple popular wireless technologies, such as Bluetooth™ (IEEE 802.15 type standards), Wi-Fi (IEEE 802.11 type standards), and other present and emerging wireless technologies would not have been feasible without the existence of such unlicensed spectrum.
Many different types of devices, including common household appliances such as Microwave ovens, RFID tags, remote control devices, security systems, Bluetooth devices, ZigBee devices, and the like operate in the ISM frequency ranges. Thus, various standards for allowing different wireless devices to both connect with each other, as well as to try to avoid interfering with each other, have evolved. For example, the standards relating to Wi-Fi include interference mitigation features.
Commercial deployments of Wi-Fi typically occupy (exclusive of guard bands) swaths of bandwidth of roughly 80 MHz in the 2.4 GHz, range (often configured in the US as eleven contiguous 20-MHz-wide and often overlapping channels with 5 MHz separation between the various channels). In the “5.8” GHz range, more bandwidth is allowed, occasionally according to a more complex and non-contiguous scheme.
In the 5.8 GHz region, originally 8 approximately 20 MHz wide channels (160 MHz bandwidth total) were allowed between 5.17 to 5.33 GH, 4 approximately 20 MHz wide channels are allowed starting at 5.49 GHz (80 MHz bandwidth total), 4 approximately 20 MHz wide channels (80 MHz bandwidth total) terminating at 5.725 GHz, and 5 approximately 20 MHz wide channels (100 MHz total) were starting at 5.735 GHz.
The U.S. now has a more unified and contiguous scheme where 37, 20-MHz non-overlapping channels are allocated between 5.17 to 5.925 GHz. If the appropriate frequencies are available for use locally, these 20 MHz wide channels can be pooled together to form larger and higher data rate carrying 40 MHz wide, 80 MHz wide, and even 160 MHz wide channels. Other countries have slightly different schemes in this region. Here this range of frequencies will be referred to generically, unless otherwise specified, as the “5.8 GHz” range.
In contrast to the very limited amount of bandwidth that was allocated to the 2.4 GHz region, substantially more bandwidth was allocated for data communication in the 5.8 GHz region. However at a given power level, the distance (range) that a given 2.4 GHz wireless signal can travel through a typical home or urban environment can be roughly twice as far as the range of an 5.8 GHz wireless signal. Thus, although Wi-Fi devices using 2.4 GHz wireless signals may be more prone to in-band interference than 5.8 GHz devices, in the absence of channel congestion a 2.4 GHz devices can have a significantly longer range than a corresponding 5.8 GHz device.
Various Wi-Fi standards, exemplified by standards such as 802.11n or 802.11acm generally allow for a Wi-Fi access point (i.e. a Wi-Fi transceiver, and potentially also a router, having a connection to a larger network such as the Internet) to announce its existence to other local Wi-Fi capable wireless devices by use of periodically transmitted beacon frames. These beacon frames transmit information about that access point, such as the access point timestamp, network capability, access service set identifier (SSID) and various other wireless parameters used by that access point. Such Wi-Fi standards also allow Wi-Fi access points and other Wi-Fi wireless devices to communicate with each other, and automatically negotiate various wireless parameters (e.g. frequencies used, data rates, modulation schemes, and the like). The standards also allow for two nearby Wi-Fi access points to automatically negotiate, to a limited extent, channel use between themselves in order to minimize interference.
In this negotiation process, the various devices involved will often keep track of various types of error rates in the exchange of various wireless data packets, and will often seek to automatically adjust various types of wireless parameters so as to minimize these error rates. Other schemes include various types of Clear-Channel Assessment (CCA) tests in which the device checks to see if a given channel is idle before transmitting, and if busy defers transmission. Still other schemes include wireless signal energy assessments and broad channel (e.g. 40 MHz) intolerance bits, which instruct nearby Wi-Fi devices to only use narrow channel (e.g. 20 MHz transmission), and the like.
For MIMO equipped Wi-Fi access points and suitable wireless devices, MIMO beamforming methods can include applying various steering matrices to steer the direction of a given wireless beam, along with various channel sounding methods such as null data packet methods. These null data packet methods, for example, operate by the use of special null data packet announcement frames and null data packet frames that an access point can send to a recipient device, and the recipient device in turn can report back information, such as a feedback matrix, that lets the access point know what MIMO beam steering direction is most favorable. The access point can then use this most favorable MIMO beam direction for subsequent communication with that particular recipient device. See, e.g., IEEE Std. 802.11n-2009, Oct. 29, 2009, published by IEEE, 3 Park Avenue, New York, and IEEE Std. 802.11ac-2013, December 2013, also published by IEEE, 3 Park Avenue, New York.